U.S. Geothermal Database Being Created

By Louise S. Durham

Geothermal energy, for many years, has proven to be an economical energy source – in select places.

A prime example is Klamath Falls, Ore., where geothermal has long been used to heat many commercial buildings, schools and more. The hot water resource even keeps the sidewalks toasty-warm to prevent snow accumulation.

Near-surface hot rocks and sufficient water are the keys to make it happen. In fact, hot subsurface rocks along with other geological factors in many tectonically active areas in the western United States – where geysers, hot springs, volcanoes and such are not uncommon – make geothermal energy economically available in certain locales.

Still, interest in this particular alternative energy source has waxed and waned over the years, pretty much in tandem with oil and gas price movements.

Currently, the Arizona Geological Survey is managing a DOE-backed three-year research program; all 50 states are participating. The $21 million program is in its second year.

The objective is to compile a National Geothermal Data System (NGDS) containing vast amounts of data. These data would be available to all those interested in developing geothermal energy resources given the declining fossil fuel reserves and increasing demand worldwide, according to AAPG member Chacko John, Louisiana Geological Survey (LGS) director and state geologist, professor-research Louisiana State University.

A Gulf Coast Context

The LGS, along with other groups, has long investigated geothermal energy along the Gulf Coast with its considerable geopressure-geothermal resource.

This is a different breed of cat from geothermal that predominates in the western United States, in that it entails large zones of hot, highly pressurized fluids in deep strata.

“The northern Gulf of Mexico geopressured-geothermal resource has been estimated by various researchers to contain from 150 to 5,000 Tcf of recoverable methane and up to 11,000 quads of thermal energy in sandstone pore fluids to a depth of 22,500 feet,” John said. “This is equivalent to many times more than the presently known conventional methane resources in the United States.”

John emphasized the geopressured-geothermal resource contains:

Chemical energy in the form of methane dissolved in pressurized brine.

Thermal energy consisting of hot brines at high temperature (225 degrees-plus F), which could be used for secondary hydrocarbon recovery or electricity generation.

Mechanical energy generated through high brine flow rates (20,000-plus barrels per day), which could be utilized to drive turbines to generate electricity.

Time for a New Look?

The DOE conducted a geopressured-geothermal research program in the northern Gulf Coast from 1975 to 1992 to gather reliable geological, engineering, environmental and economic information about this resource to ascertain its viability for development.

LGS participated in the program, which included industry, universities and national laboratories.

Four wells were drilled and tested, and the oil and gas industry donated another 12 wells, which also were tested.

John, in noting how much valuable information came out of this program, said the time is right to revisit some of the results given the current interest in alternative energy resources. (He and LGS colleagues had presented a poster session summarizing the program at the 2006 GCAGS meeting in Lafayette, La.)

The program participants identified geopressured and geothermal fairways in Louisiana and Texas. They demonstrated that:

High brine flow rates of 20,000 to 40,000 barrels per day are possible for long periods of time.

Used brine could be re-injected into sands below fresh-water aquifers without contamination.

Inhibitors controlled corrosion and scaling.

A hybrid power system generated electricity using both separated methane and geothermal heat.

Profitable commercial development of geopressure-geothermal was not feasible at that time, but the world’s energy picture today is far more favorable for unconventional, alternative energy source development, he noted.

Indeed, information derived from the early DOE-sponsored program played a key role in laying the foundation for current interest and activity.

A favorable aspect of the Gulf Coast is that the many existing deep depleted and/or dry wells in the northern Gulf of Mexico basin can be used to extract gas from brine, thereby saving well drilling costs.

John pointed out that geothermal has myriad potential applications other than generating electricity. These include enhanced oil recovery, aquaculture, greenhouses/agriculture and hybrid power systems, among others.